referenced to the return terminal of the 24V input bus. There
are two versions of the
PowerQor series converter that differ
by the sense of the logic used for the ON/OFF input. In the
PQxxyyyQGAzzPxx version, the ON/OFF input is active
high (meaning that a high turns the converter
on). In the
PQxxyyyQGAzzNxx version, the ON/OFF signal is active
low (meaning that a low turns the converter
on). Figure A
details five possible circuits for driving the ON/OFF pin.
Figure B shows detail of the internal ON/OFF circuitry.
Pins 7 and 5 (SENSE(+)): The SENSE(+) inputs correct
for voltage drops along the conductors that connect the con-
verter’s output pins to the load.
Pin 7 should be connected to Vout(+) and Pin 5 should be
connected to Vout(-) at the point on the board where regu-
lation is desired. That is,
[Vout(+) - Vout(-)] – [SENSE(+) - SENSE (-)] < 10%Vout
Pins 7 and 5 must be connected for proper regulation of the
output voltage. However, if these connections are not made,
nothing catastrophic will happen to the converter under nor-
mal operating conditions—the converter will simply deliver
an output voltage that is slightly higher than its specified
value.
Note: the output over-voltage protection circuit senses the
voltage across the output (pins 8 and 4) to determine when
it should trigger, not the voltage across the converter’s sense
pins (pins 7 and 5). Therefore, the resistive drop on the
board should be small enough so that output
OVP does not
trigger, even during load transients.
Pin 6 (TRIM): The TRIM input permits the user to adjust the
output voltage across the sense leads up or down. To lower
the output voltage, the user should connect a resistor
between Pin 6 and Pin 5, which is the SENSE(-) input. To
raise the output voltage, the user should connect a resistor
between Pin 6 and Pin 7, which is the SENSE(+) input.
A resistor connected between Pin 6 and Pin 5 will decrease
the output voltage. For a desired decrease of
percent of
the nominal output voltage, the value of this resistor should
be
Product # PQ24018QGA25
Phone 1-888-567-9596
Doc.# 005-2QG218D_A
3/1/02
Page 9
Technical Specification
24Vin 1.8Vout 25A
Quarter
Brick
Open Collector Enable Circuit
Figure A: Various circuits for driving the ON/OFF pin.
Remote Enable Circuit
Direct Logic Drive
Negative Logic
(Permanently Enabled)
Positive Logic
(Permanently Enabled)
ON/OFF
Vin(_)
ON/OFF
Vin(_)
ON/OFF
5V
TTL/
CMOS
Vin(_)
ON/OFF
Vin(_)
Rtrim-down =
(
511) - 10.22
%
(k
)
=
(VNOM – VDES) x 100%
VNOM
where
VNOM = Nominal Voltage
VDES = Desired Voltage
and
Figure B: Internal ON/OFF pin circuitry (detail)
TTL
5V
50k
100k
Vin(+)
ON/OFF
Vin(_)
50k
100pF